You’d think two cars sharing what is fundamentally the same engine would feel very similar, right? Not in the case of the Mercedes-Benz SL63 AMG and its supercar brother, the SLS AMG: these are two different beasts as you can see from our hands-on with that monster. But what if your taste is for something a bit less, well, in your face?

Well if you ask that question to Mercedes, it would point you to the car you can see at the top of the page. Same twin-turbo V8 punch, slightly more velvet glove wrapper. If we were being unfair (and sexist), we’d say the SL is the footballer’s wife to the SLS’s very Premier League footballer.

But before you start to scoff at that idea, dismiss the SL at your peril, because it has the on-paper potential to be the less obvious, but much more clever choice. If we forget about the odd thousand pounds between friends and round up prices, the SL is effectively half the price of the SLS, but it never comes across as being only half the car.

For a start, the first time I pin the throttle on the slip road leading to the A3, there’s the same "Oh my god, hold on to the steering wheel for dear life, because the world’s going backwards" acceleration that you get in the SLS.

But we will be honest, the SLS does feel ever so slightly more rapid and scary. Partly that’s a trick of the audio phonics, because the exhaust note on the SLS is angry, crackling and hissing from the off, whereas on the SL it’s relatively docile unless you really hammer it. And partly this sense is because – as we’re comparing it the SLS roadster, with the roof down, you’re a good bit more ensconced in the SL than in its big brother. It’s like this car’s plush, vented, heated and twin-stitched leather seats are wrapping their way around you in a protective embrace.

Pop up the built-in retractable wind deflector that’s hidden behind your head and you can have a phone conversation, roof down, at UK motorway speeds – it’s that refined. And just in case you weren’t feeling soothed enough, Mercedes offers you the innovation of "Airscarf" - a ventilation system that gently blows warm air out of the top of the seat around your neck to provide an insulating buffer of warmth from chill winds.

Still not relaxed enough? Then how about switching on either the heating, venting or massaging functions of the two front seats. Or activating the brilliant Distronic Plus with pre-safe break – also available on much “lowlier” Mercs - it’s the company’s name for radar guided cruise control.

Pop up the folding hardtop roof and you’re essentially in a coupe. But while it’s tempting to rag around everywhere with the roof down, given the various devices that have been designed to insulate you from outside, doing so means you miss what’s actually our favourite trick on this car: the variable transparency roof – or Panoramic vario-roof with Magic Sky Control in Merc marketing speak. The main roof panel that sits above your head is adjustable between almost totally opaque and clear-glass transparent. A button on the header rail puts a piezo-electric charge through it and allows you to completely alter the ambience in the cabin – a neat feature and nice party trick to show off to your passenger.

The IWC timepiece buried in the top of the dash is worthy of a mention too. Bentley’s long done similar in a brand tie up with Brietling, so the IWC inserting is pertinent – indicative of the lofty status and positioning Mercedes intends for this car.

Naturally, the SL63 comes with an almost infinitely variable drive setup system, but Merc handily groups these into C (for comfort), S (for sport) S+ (you get the idea). Which means that you’ve the choice of wafting around in almost put-yourself-to-sleep levels of ride comfort and gearbox slushiness, or scare-your-self witness gun-crack like bangs from the exhaust as the gearbox smashes home the next gear under full bore acceleration.

But our favourite trick of the SL63’s was that, left in standard mode, it uses stop start to kill this might mighty motor at the traffic lights. It might help you use slightly less than the gallon of fuel about every 11 miles that we managed on what was an admittedly rather adrenalin-fuelled rush around Surrey, too.

Gripes? Well, like the SLS, while we prefer Mercedes’s Comand system to almost every other touchscreen system, and we love the clarity of the digital screen in the centre of the speedo, the main interface and centre screen aren’t the last word in either user-interface menu simplicity, or graphical quality - why the yellow contrast colour background, Benz?

And while some might argue that looks are in the eye of the beholder, we’d argue that good design is good design – and if we’re being honest the SL seems to have lost its way somewhat. It’s turned into a rather lumpen and slightly unharmonious set of exterior forms, which is a shame, because if you look down the back catalogue of this model line, the SL - think Bobby Ewing and Dallas in the Eighties to name just one previous version - might have been in with a shout of "prettiest model line of any car in history" award. The new one rather kills any notion of that. Still, at least we can tell it apart from the previous model, which is more than can be said for the new Audi A3.

So, to our original point, is the SL just Surrey champagne parties, or proper Premier League with the odd midweek trip to Europe for the Champions League thrown in? It’ll be pigeonholed as the former, leaving reasonable space for its bigger and much more expensive brother the SLS to do the shouty, exuberant personality thing of the latter. Which is a shame because, with the exception of the way it looks, this is an extraordinarily impressive car – one that can play happily in the supercar sandpit one minute and then waft you easily to the Cote d’Azur the next.

For refinement, features, interior ambience and tech it absolutely trounces a Jag XKR-S, which is probably its closest opposition, leaving only BMW’s M6 Convertible as its true challenger. We’re yet to drive the men from Munich’s new performance range-topper, but it’ll have to be an impressive car to beat the SL63. It’s a true iron fist, velvet glove of a car.